Why doesn’t “CLEAR DATA” button actually clear all the Cookies, Site Data, or Cache for a period of time? Why doesn’t “Delete cookies and site data when FF closes” clear all junk?

I want to tell you why I almost never do the updates FF always asks me to do. • NOTE: I never set ANY PROGRAM to do automatic updates. I don’t want them slowing down or interrupting my system when I’m trying to get something done. I’ll decide when. • It seems like FF does updates WAY TOO FREQUENTLY. • THE MAIN PROBLEM – After the 1st to 5th update, there will always be about 30k to 60k of Cookies, Site Data, or Cache that will not clear when I select “CLEAR DATA” in the “Cookies and Site Data” section of “Privacy & Security”. What the heck; how can I be sure that it isn’t something that does not belong on my system? Maybe it’s something FF requires, but there is no way of knowing that, and no way of knowing what it is. • THE SECOND PROBLEM - Even though I always select to “Delete cookies and site data when FF closes”; FF does not automatically clear all of that junk. I always have to go in and manually do it. Seems to mostly happen if I’ve been on facebook, but they are not exclusive. I thought FF is supposed to be a secure way of being on the net? Perhaps that does not apply to certain web services or vendors. Perhaps that does not apply to whatever it is that the FF program will not allow me to clear from Cookies, Site Data, or Cache. If I'm wrong please let me know, otherwise please forward to FF to hopefully fix.